a guy on a DTV I know, asked for the requirements for the extension on Immigration Hua Hin. They listed about similar requirements than the ones you mentioned, but what was added to this was their requirement that the 500,000 THB must sit in a Thai bank account in his sole name. Since you cannot open a bank account on a DTV visa without greasing the palms of an agent, because it is a tourist visa type, this is the typical Catch22 situation. So he decided to just do the border bounce and get stamped the next 180 days, no questions asked
you better book with a listed and licensed hotel. AirbnB rentals under 30 days are illegal, except the landlord has a hotel license (which they rarely have)
i am not talking about the requirement to obtain the DTV. I am talking about the requirement to obtain the 180-days extension of the DTV on Immigration. THEY might want to see the 500.000 on a THAI bank account